Breast Cancer is the most frequent malignancy diagnosed in women in the United States and the second leading cause of cancer related mortality in women. Metastasis to distant organs continues to be the greatest obstacle to eradication of this malignancy. Greater understanding of the biological processes that contribute to tumor progression will lead to development of effective therapies against this disease. The insulin receptor substrate (IRS) proteins are important signaling intermediates downstream of the Insulin-like growth factor (IGF-1) receptor and they play a crucial role in the response of tumor cells to IGF-1 stimulation. The two IRS proteins expressed in mammary epithelial cells, IRS1 and IRS2, play different roles in breast cancer. Specifically, tumors that express IRS2 are highly metastatic in comparison to IRS-1 expressing tumors. In addition, IRS2 staining at the membrane in patient tumor samples correlates with decreased overall survival. Studies from our group have identified an IRS2-specific interaction with the microtubule cytoskeleton and demonstrated that disruption of microtubules leads to a decrease in PI3K/Akt activation downstream of IRS2. These findings in conjunction with our preliminary data suggest that the subcellular localization of the IRS proteins plays an important role in their cellular functions. Te work the applicant proposes will explore the potential role of IRS2-microtubule interactions in breast cancer progression, specifically addressing the requirement of this interaction for invasion, glycolysis, PI3K/Akt signaling and tumor metastasis. Our goal with this proposal is to take a molecular biology approach to elucidate the importance of IRS2-microtubule interactions in IRS2 mediated functions (Aim 1). Furthermore, we will use animal models to study the significance of this interaction for tumor progression to metastasis and the impact of IRS2 function on tumor response to IGF-1 receptor inhibitors (Aim 2). The studies proposed in this application will enhance our understanding of the importance of IRS2 in breast cancer progression. Additionally, our results can provide the rationale for the development of novel therapeutic approaches for the treatment of IRS2-dependent malignancies.